DinosaurTales, I agree with you, it can be tough following the strict guidelines of your teacher. And each teacher has different views, when playing Bach I make a lot of dynamic changes, but not tempo changes. However, your teaher's take on it, in some little way will benefit you, coordiation and finger strength for sure. I think it is important to follow the teachers guidelines, so you can get from the piece what they think is important, and as soon as they or you leave--play it your way :-)
We need the teacher to point us in the right direction, so we can learn appropriate ways to interpret things. And, there are appropriate ways to interpret things, just like in Writing...write what ever you want as long as you follow some sort of form of grammer.
Frederic, I agree with you, Bach music is very broad in terms of interpretion.